1. Field of the Invention
This invention relates to novel coating compositions which are capable of protecting the interior surfaces of chimney liners, flue ducts, and the like from the effects of corrosive substances that are encountered in many of today's industrial locations such as power plants and smelters.
A combination of factors have changed the conditions under which chimneys in such locations as power plants and smelters operate, and have made the problem of corrosion, particularly, acid corrosion, more critical. For example, as the supply of clean burning fuels has decreased, lower quality fuels having higher sulfur contents have been substituted. The combustion of these lower quality fuels results in the production of flue gases which contain corrosive substances, especially sulfur-containing substances. At the same time, utility companies have increased the efficiency of heat utilization so that the temperatures of the flue gases produced have dropped closer to the acid due points. Finally, installations equipped with sulfur dioxide scrubbers produce flue gases which are not only cooler but wetter and consequently discharge a corrosive mist into the lower reaches of the chimney liners. Because of such factors efforts have been undertaken to develop coating compositions which are capable of protecting the surfaces of chimney liners, scrubbers and flue ducts from the corrosive and/or deteriorating effects of substances which come into contact with these surfaces during the operation of power plants, smelters and the like.
2. Description of the Prior Art
In order to combat the problem of surface corrosion of chimney linings, flue ducts, etc., various plastic coatings have been developed for use in protecting their interior surfaces which are typically composed of steel, concrete or brick. One approach has involved the use of a coating layer which includes a polymeric material such as a polyester or a vinyl ester and a reinforcing filler material such as glass flakes.
Another approach has involved the use of a fluoroelastomer as a coating layer. This approach is based in part on such prior art techniques as those of U.S. Pat. No. 3,526,532, which discloses the use of a hydrofluorocarbon coating layer overlaid on a polymeric primer coating as imparting corrosion resistance to a coated metal surface. One such coating is Colebrand CXL2000 developed by Colebrand Ltd., London, England and marketed in the United States by Pullman Power Products, Williamsport, Pennsylvania.